This invention relates in general to improved seal means for drill bit bearings and in particular to seal means which demonstrate improved accommodation for axial, radial and angular displacements of the roller cutter.
Earth boring drill bits, such as are typically employed in the petrochemical industry for drilling oil or gas wells, are rugged pieces of equipment which must operate in very severe environments. In such operations, a drill bit is typically threaded onto a section of pipe and lowered into a well bore wherein it is rotated for the purpose of cutting through rock and earth formations. Rotatable cutters are usually mounted on a shaftlike cutter support and the fragments of rock created by the operation of the rolling cutters are removed from the well bore utilizing a drilling fluid or "mud" solution. In prior art drill bit bearings, several solutions have been proposed to inhibit the ingress of abrasive detritus into the bearings of the roller cutter thereby permitting the roller cutter to be operated over extended periods of time in this environment. One such solution to this problem has been the utilization of pressurized lubricant reservoirs which are operated by the pressures of the drilling fluid within the well bore and serve to equalize the pressure of the lubricant being forced onto the bearing surfaces. This pressurized lubricant reservoir has been moderately successful in preventing the ingress of abrasive detritus into the bearing area; however, the pressurized lubricant reservoir does result in the egress of lubricant from the bearing area in greater amounts than is normally experienced.
Another approach to the problem of preventing abrasive material from wearing away at the bearing surface has been the utilization of various packing ring sealing apparatus. An early example of this approach may be seen in U.S. Pat. No. 3,397,928, issued to Edward M. Galle, which utilizes the simple expedient of an elastomeric sealing ring which has been compressed between the inner face between the roller cutter shaft. Another example of a packing ring seal utilized in rotary drill bits may be seen in U.S. Pat. No. 3,656,764, issued to William P. Robinson. The Robinson drill bit seal assembly utilizes two elastomeric O-ring seals which are separated by a rigid ring which is utilized to seat the O-rings into opposing bearing surfaces. This utilization of a rigid ring, while providing an increase in accommodation of radial, axial and angular displacements over previously known 0-ring seals, is still limited in the amount of such displacement which may be accommodated.
Each of these sealing mechanisms and pressurized lubrication systems is designed to prevent the ingress of abrasive detritus into the bearings supporting the roller cutters. This is necessary since it is most desirable to operate the drill bit for long periods of time between drill bit changes, due to the amount of manpower and time required to remove the drill stem from the well bore to replace the drill bit. Complicating this problem is the fact that the fluctuations in position and pressure which are encountered by an earth boring drill bit during operation are substantial and tend to displace the roller cutter from the shaft upon which it is mounted. These displacements from normal mounting position increase as the bearing surface is worn and it is most desirable to utilize a sealing mechanism which can accommodate these increasing fluctuations in position without deteriorating to the point where abrasive material may enter the bearing surface or undue amounts of lubricant are lost.